When AT&T announced that it would purchase BellSouth, it agreed to a few conditions to get government approval.

One was to sell wireless broadband licenses held by BellSouth. The spectrum is good for rolling out technologies like WiMax, something both Sprint Nextel and Kirkland-based Clearwire pledge to do on a nationwide basis.

At the time, news reports said that Sprint Nextel was the likely bidder for the spectrum. I speculated here that Clearwire would most likely be the winner.

Today, AT&T announced that it would sell the spectrum to Clearwire. Prior to the merger between AT&T and BellSouth, BellSouth was offering wireless broadband in parts of 15 cities in eight states.

I could guess why Clearwire was the winner. The FCC did not require any conditions to the sale, so BellSouth was likely sell it to the least-threatening buyer. Or, perhaps, sell to the buyer to which it has the closest ties. That could be Clearwire, whose founder Craig McCaw also started McCaw Cellular Communications, which later became AT&T Wireless. Cingular Wireless, which bought AT&T Wireless in 2004, is now owned entirely by AT&T (and now called AT&T).

AT&T said today the transaction is worth $300 million in cash. It is expected to close promptly, following government approvals.

Clearwire has filed to go public, and updated its filings with the SEC last week to say that it now expects to raise up to $575 million. Two months ago, it was seeking to raise about $400 million.